In various optical transmission systems, it can be useful for digital data to be converted to analog form for processing and/or transmission. The use of optical technology for implementing digital to analog (D/A) converters can have various advantages, including, for example, high-speed clocking and signal sampling, wide-bandwidth, and light-weight components, among others.
A previous approach to optical D/A conversion involves using several electronic D/A converters to convert digital data into an electrical analog signal. The electrical analog signal is then applied to an optical modulator of a laser to impress the electrical analog signal onto the intensity of light at a single wavelength. As such, this method can involve the use of many separate electronic D/A converters as well as many optical modulators and/or lasers in order to provide an optical analog signal at a number of different wavelengths.
Another approach to optical D/A conversion involves splitting light from an optical source evenly into many mutually coherent optical beams. In this approach, the light associated with each mutually coherent beam is phase shifted according to digital data and is passed to a combiner element which merges the light back into a single fiber. The interference associated with the phase shifted mutually coherent beams affects the intensity of the light and generates an analog signal for a particular wavelength. As such, this method can be limited to coherent optical sources and can involve the use of multiple different coherent optical sources and numerous optical components in order to produce analog signals at different wavelengths.